Comparison of calculation result of 3 bus and 5 bus equivalent system

• Check for the difference in calculation with 5 bus and 3 bus equivalent system when calculating transient problems TRV, MOV ...=> From there, it is clear that the need to calculate tra

Tp HCM, September, 2020

1 PURPOSE

• Check for the difference in calculation with 5 bus and 3 bus equivalent system when calculating transient problems (TRV, MOV )

=> From there, it is clear that the need to calculate transient problems with a large system in order to increase the reliability and accuracy of the results.

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1 PURPOSE

2 THEORETICAL BASIS

• Thevenin's theorem allows to replace a complex circuit with a simple circuit consisting of only one source and one resistor.

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2 Theoretical basis

2.1 Thevenin's theorem

Using Thevenin's theorem is especially advantageous when:

• Focus on a specific part of a circuit The rest of the circuit can be replaced with a simple Thevenin equivalent circuit.

• Using the Thevenin equivalent avoids having to analyze complex circuits.

2 Theoretical basis

2.2 The purpose of Thevenin’s theorem

• Thevenin's theorem does not apply to circuits containing nonlinear elements

• Circuit equivalence according to Thevenin's theorem cannot be equivalent in terms of electromagnetic induction between components in the power system.

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2 Theoretical basis

2.1 Thevenin’s theorem limitations

• For transient problems, the Thevenin’s equivalent model can not be applied Because the wave re-reflection (standing wave) will occurs due to the large system equivalence to the smaller system The larger the simulation system, the smaller the amplitude of the reflected wave becomes.

n=6 bus

Standing waves based on simulation system

2 Theoretical basis

2.1 Limitations when using Thevenin’s equivalent

• Volt-Ampe characteristics when calculating with circuits with nonlinear elements before and after Thevenin equivalent

3 CALCULATION MODEL

3 Calculation model

3.1 Calculation model

• Calculated with normal operation mode in 2020

• Calculation using EMTP software

• The 3 buses equivalent system model includes Doc Soi, Pleiku 2 and Quang Trach

Zth Zth

Zth

• The 5 buses equivalent system model includes Doc Soi, Pleiku 2, Quang Trach,

Thanh My and Da Nang

Zth

Zth Zth

3 Calculation model

3.2 Transposed in 500kV Doc Soi – Pleiku 2 transmission line

3 Calculation model

3.2 Transposed in 500kV Quang Trach – Doc Soi transmission line

3 Calculation model

3.3 Calculation fault points

Zth Zth

• Calculation of absorbed energy level of MOV with fault points 1,2,3 on the Doc Soi, Pleiku 2 and Quang Trach

Zth

2

3 CALCULATION RESULT

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2 phase short circuit-CB

Doc Soi 3 phase short circuit-CBDoc Soi 2 phase short circuit-CBPleiku 2 3 phase short circuit-CBPleiku 2

1.6

1.8

22.2

2.4

2.6

2 phase short circuit-CB

Doc Soi 3 phase short circuit-CBDoc Soi 2 phase short circuit-CBPleiku 2 3 phase short circuit-CBPleiku 2

0.168

0.106

0.4070.547

2 phase short circuit-CB Doc

Soi 3 phase short circuit-CB DocSoi 2 phase short circuit-CBPleiku 2 3 phase short circuit-CBPleiku 2

2 phase short circuit-CB Doc

Soi 3 phase short circuit-CB DocSoi 2 phase short circuit-CBPleiku 2 3 phase short circuit-CBPleiku 2

3 phase short-circuit at Quảng Trạch

3 Bus system 5 Bus system

1 phase short-circuit at Quảng Trạch

3 Bus system 5 Bus system

4 Calculation Result

4.3 Comparison of MOV calculation result

3 phase short-circuit at Pleiku 2

3 Bus system 5 Bus system

1 phase short-circuit at Pleiku 2

3 Bus system 5 Bus system

5 COMMENTS ON THE CALCULATION RESULTS

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5 COMMENTS ON THE CALCULATION RESULTS

From the calculation results we have the following comments

• The difference in the TRV, RRRV calculation results between the equivalent system of 3 bus and 5 bus is about 30%.

• The difference in the MOV calculation results between 3 bus and 5 bus equivalent systems is very large (about 100%).

→ The wave-related transient problems (MOV computation) give very different results when the system equivalents are 3 and 5 bus Similar to the results of TRV calculation, RRRV also has a relative difference when calculating with the equivalent system of 3 bus and

5 bus.

• W Richter, "Applications of Thevenin's theorem," in Electrical

Engineering, vol 64, no 3, pp 103-105, March 1945, doi:

10.1109/IEEE.1945.6440897.

• A W Love, "Comment on "Limitations of the Thevenin and Norton

equivalent circuits for a receiving antenna"," in IEEE Antennas and

Propagation Magazine, vol 45, no 4, pp 98-99, Aug 2003, doi:

10.1109/MAP.2003.1241317.

• Transient Analysis of Power Systems: Solution Techniques, Tools and

Applications, First Edition.

Edited by Juan A Martinez-Velasco.

Annex B - Dynamic System Equivalents

• https://en.wikipedia.org/wiki/Th%C3%A9venin%27s_theorem

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REFERENCES DOCUMENT

EVN PECC2